Friday, April 15, 2005

What's your blood type?

I'm a big fan of Richard Dawkins, author of The Selfish Gene and other good science books. Just finished his latest book, The Ancestor's Tale, all 600-plus pages. Yet another good book if you're into that science/evolution kind of thing. A little heavier into the explanation of how science is done than I need, but some people will like those parts, and the rest of us can skip to what they learned as a result.

Some random thoughts:

*Do you have type A, B, or O blood? I have type A blood, determined by a certain gene in my DNA, a gene that has a shared common ancestor with everyone else with type A blood. If your gene gave you type B or type O blood, that gene is also related to me, but only in a far more distant common ancestor that diverged into the three types. Here's the fascinating thing Dawkins points out: chimps also have type A, B, and O blood. The divergence into different genes long preceded our species' divergence, six million years ago. As far as my type A gene is concerned, it's more closely related (maybe I'm more closely related) to a chimp with type A blood than a human with type B blood. Wrap your mind around that.

*Another relationship that's surprising: sharks, trout, and us - which two of the three are most closely related? George Bush and a rainbow trout have a more recent common ancestor than the rainbow trout has with Jaws.

*Dawkins describes an evolutionary arms race between species as a kind of treadmill where no one gets ahead: prey get faster, predators get faster. Predators develop venom, prey develop venom resistance. Dawkins says there is no way to call a truce in the race, according to the rules of natural selection. I'm not sure that's completely true though. At a certain point, the efficiency trade-off in the arms race is outweighed by putting effort in other directions that could actually reduce the arms race. Territorial predators spend energy and risk death by excluding and killing other predators, when the predators could be hunting prey and having more babies. The prey species, facing reduced pressure, survives by getting better at growing and reproducing, more so than by getting better at evading predators. Another example would be trees converting leaf-eating monkeys into fruit-eating monkeys, or parasites converting into symbiotes. I expect Dawkins wouldn't disagree with this, but just say it's obvious that no trend can go on forever.

One more thought about the arms race: to the extent it's true, you should expect populations of both species to decrease. It takes more energy to conduct a hunt at 40 miles an hour than at 20 miles an hour. Resources spent on the chase, on building heavier body armor or stronger fangs than one's ancestors have to come at a price - you either get worse at something else, or you have fewer babies. This seems like it should be a testable proposition over a broad range of species, at least in theory.